Thread: Regarding rotation of seismogram for right handed system

Started: 2020-10-27 10:19:37
Last activity: 2020-12-04 10:28:58
Topics: SAC Help
sanjay Singh Negi
2020-10-27 10:19:37
Hi Sac users,
I have OBS record that follows the right-handed
system in which H2 component is 90 degree counter-clockwise of H1.

Horizontal component data file are as following:
2018.128.01.00.45.420.X.sac ---> East component
2018.128.01.00.45.420.Y.sac ----> North component
2018.128.01.00.45.420.Z.sac ----> Vertical component

The orientation correction angle is 80 degree.

For rotation, I use the following scheme:
sac>> read 2018.128.01.00.45.420.Y.sac 2018.128.01.00.45.420.X.sac
sac>> rotate to 80 reverse


Could you please comment on whether the command I give is correct or not?
Why I am confused about rotation is because of two following reasons:

1: To get true north-south rotation for an OBS record the orientation
correction of 80 degrees has to be made. For this, logically -80/360-80
degree should be implemented to rotate it back to North-South. Would +80
degree be fine?

2. What exactly sac does on applying reverse at the end of rotate command?

Thanks in advance.

Regards
Sanjay

  • Hello Sanjay,
    Based on the SAC documentation, your description of components, and
    assuming that your
    orientation correction is clockwise from north (+80?, how did you estimate
    this?), it seems that "rotate to -80 reverse" is correct.

    "Reverse" indicates that H2 is pointing north and H1 is pointing east: the
    second component is lagging the first by 90°. Think of it as the reverse
    convention as, usually, H1 and H2 are pointing north and east respectively.

    http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

    Januka

    On Tuesday, 27 October 2020, sanjay Singh Negi (via IRIS) <
    sac-help-bounce<at>lists.ds.iris.edu> wrote:

    Hi Sac users,
    I have OBS record that follows the right-handed
    system in which H2 component is 90 degree counter-clockwise of H1.

    Horizontal component data file are as following:
    2018.128.01.00.45.420.X.sac ---> East component
    2018.128.01.00.45.420.Y.sac ----> North component
    2018.128.01.00.45.420.Z.sac ----> Vertical component

    The orientation correction angle is 80 degree.

    For rotation, I use the following scheme:
    sac>> read 2018.128.01.00.45.420.Y.sac 2018.128.01.00.45.420.X.sac
    sac>> rotate to 80 reverse


    Could you please comment on whether the command I give is correct or not?
    Why I am confused about rotation is because of two following reasons:

    1: To get true north-south rotation for an OBS record the orientation
    correction of 80 degrees has to be made. For this, logically -80/360-80
    degree should be implemented to rotate it back to North-South. Would +80
    degree be fine?

    2. What exactly sac does on applying reverse at the end of rotate command?

    Thanks in advance.

    Regards
    Sanjay




    --
    Januka Attanayake
    Research Fellow | Earthquake Seismology
    Homepage: *https://sites.google.com/site/janukaattanayake
    https://sites.google.com/site/janukaattanayake*

    School of Earth Sciences | McCoy Bldg. 200
    University of Melbourne | Parkville 3010 VIC
    Australia

    • Sanjay

      To convert right-handed system into left-haded, you will need to flip the vertical component.
      For a high-handed system, positive vertical points down.

      -John


      On Oct 27, 2020, at 5:11 AM, Geo . (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:

      [This email originated from outside of OSU. Use caution with links and attachments.]

      Hello Sanjay,
      Based on the SAC documentation, your description of components, and assuming that your
      orientation correction is clockwise from north (+80?, how did you estimate this?), it seems that "rotate to -80 reverse" is correct.

      "Reverse" indicates that H2 is pointing north and H1 is pointing east: the second component is lagging the first by 90°. Think of it as the reverse convention as, usually, H1 and H2 are pointing north and east respectively.

      http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

      Januka

      On Tuesday, 27 October 2020, sanjay Singh Negi (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:
      Hi Sac users,
      I have OBS record that follows the right-handed system in which H2 component is 90 degree counter-clockwise of H1.

      Horizontal component data file are as following:
      2018.128.01.00.45.420.X.sac ---> East component
      2018.128.01.00.45.420.Y.sac ----> North component
      2018.128.01.00.45.420.Z.sac ----> Vertical component

      The orientation correction angle is 80 degree.

      For rotation, I use the following scheme:
      sac>> read 2018.128.01.00.45.420.Y.sac 2018.128.01.00.45.420.X.sac
      sac>> rotate to 80 reverse


      Could you please comment on whether the command I give is correct or not?
      Why I am confused about rotation is because of two following reasons:

      1: To get true north-south rotation for an OBS record the orientation correction of 80 degrees has to be made. For this, logically -80/360-80 degree should be implemented to rotate it back to North-South. Would +80 degree be fine?

      2. What exactly sac does on applying reverse at the end of rotate command?

      Thanks in advance.

      Regards
      Sanjay




      --
      Januka Attanayake
      Research Fellow | Earthquake Seismology
      Homepage: https://sites.google.com/site/janukaattanayake

      School of Earth Sciences | McCoy Bldg. 200
      University of Melbourne | Parkville 3010 VIC
      Australia





      ----------------------
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      Topic home: http://ds.iris.edu/message-center/topic/sac-help/ | Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

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      • sanjay Singh Negi
        2020-10-28 18:28:05
        Hi John,
        I never thought about it, but logically it seems correct.
        It means that in order to flip, I need to rotate the vertical component to
        180 degrees.
        Thanks,
        Sanjay


        On Wed, Oct 28, 2020 at 1:31 AM Nabelek, John (via IRIS) <
        sac-help-bounce<at>lists.ds.iris.edu> wrote:

        Sanjay

        To convert right-handed system into left-haded, you will need to flip the
        vertical component.
        For a high-handed system, positive vertical points down.

        -John


        On Oct 27, 2020, at 5:11 AM, Geo . (via IRIS) <
        sac-help-bounce<at>lists.ds.iris.edu> wrote:

        [This email originated from outside of OSU. Use caution with links and
        attachments.]

        Hello Sanjay,
        Based on the SAC documentation, your description of components, and
        assuming that your
        orientation correction is clockwise from north (+80?, how did you
        estimate this?), it seems that "rotate to -80 reverse" is correct.

        "Reverse" indicates that H2 is pointing north and H1 is pointing east:
        the second component is lagging the first by 90°. Think of it as the
        reverse convention as, usually, H1 and H2 are pointing north and east
        respectively.

        http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

        Januka

        On Tuesday, 27 October 2020, sanjay Singh Negi (via IRIS) <
        sac-help-bounce<at>lists.ds.iris.edu> wrote:
        Hi Sac users,
        I have OBS record that follows the right-handed
        system in which H2 component is 90 degree counter-clockwise of H1.

        Horizontal component data file are as following:
        2018.128.01.00.45.420.X.sac ---> East component
        2018.128.01.00.45.420.Y.sac ----> North component
        2018.128.01.00.45.420.Z.sac ----> Vertical component

        The orientation correction angle is 80 degree.

        For rotation, I use the following scheme:
        sac>> read 2018.128.01.00.45.420.Y.sac 2018.128.01.00.45.420.X.sac
        sac>> rotate to 80 reverse


        Could you please comment on whether the command I give is correct or not?
        Why I am confused about rotation is because of two following reasons:

        1: To get true north-south rotation for an OBS record the orientation
        correction of 80 degrees has to be made. For this, logically -80/360-80
        degree should be implemented to rotate it back to North-South. Would +80
        degree be fine?

        2. What exactly sac does on applying reverse at the end of rotate
        command?

        Thanks in advance.

        Regards
        Sanjay




        --
        Januka Attanayake
        Research Fellow | Earthquake Seismology
        Homepage: https://sites.google.com/site/janukaattanayake

        School of Earth Sciences | McCoy Bldg. 200
        University of Melbourne | Parkville 3010 VIC
        Australia





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        --



        Sanjay Singh Negi
        Alternate Email: sasnegi85<at>gmail.com

        Contact No.- +91-9536145596


        • Just multiply by -1.


          On Oct 28, 2020, at 5:58 AM, Sanjay Singh Negi <sonoogeo<at>gmail.com> wrote:

          [This email originated from outside of OSU. Use caution with links and attachments.]

          Hi John,
          I never thought about it, but logically it seems correct.
          It means that in order to flip, I need to rotate the vertical component to 180 degrees.
          Thanks,
          Sanjay


          On Wed, Oct 28, 2020 at 1:31 AM Nabelek, John (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:
          Sanjay

          To convert right-handed system into left-haded, you will need to flip the vertical component.
          For a high-handed system, positive vertical points down.

          -John


          On Oct 27, 2020, at 5:11 AM, Geo . (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:

          [This email originated from outside of OSU. Use caution with links and attachments.]

          Hello Sanjay,
          Based on the SAC documentation, your description of components, and assuming that your
          orientation correction is clockwise from north (+80?, how did you estimate this?), it seems that "rotate to -80 reverse" is correct.

          "Reverse" indicates that H2 is pointing north and H1 is pointing east: the second component is lagging the first by 90°. Think of it as the reverse convention as, usually, H1 and H2 are pointing north and east respectively.

          http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

          Januka

          On Tuesday, 27 October 2020, sanjay Singh Negi (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:
          Hi Sac users,
          I have OBS record that follows the right-handed system in which H2 component is 90 degree counter-clockwise of H1.

          Horizontal component data file are as following:
          2018.128.01.00.45.420.X.sac ---> East component
          2018.128.01.00.45.420.Y.sac ----> North component
          2018.128.01.00.45.420.Z.sac ----> Vertical component

          The orientation correction angle is 80 degree.

          For rotation, I use the following scheme:
          sac>> read 2018.128.01.00.45.420.Y.sac 2018.128.01.00.45.420.X.sac
          sac>> rotate to 80 reverse


          Could you please comment on whether the command I give is correct or not?
          Why I am confused about rotation is because of two following reasons:

          1: To get true north-south rotation for an OBS record the orientation correction of 80 degrees has to be made. For this, logically -80/360-80 degree should be implemented to rotate it back to North-South. Would +80 degree be fine?

          2. What exactly sac does on applying reverse at the end of rotate command?

          Thanks in advance.

          Regards
          Sanjay




          --
          Januka Attanayake
          Research Fellow | Earthquake Seismology
          Homepage: https://sites.google.com/site/janukaattanayake

          School of Earth Sciences | McCoy Bldg. 200
          University of Melbourne | Parkville 3010 VIC
          Australia





          ----------------------
          SAC Help
          Topic home: http://ds.iris.edu/message-center/topic/sac-help/ | Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

          Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
          Update subscription preferences at http://ds.iris.edu/account/profile/



          ----------------------
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          Topic home: http://ds.iris.edu/message-center/topic/sac-help/ | Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

          Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
          Update subscription preferences at http://ds.iris.edu/account/profile/


          --



          Sanjay Singh Negi
          Alternate Email: sasnegi85<at>gmail.com

          Contact No.- +91-9536145596



          • sanjay Singh Negi
            2020-10-28 22:55:33
            Thank you for the correction.

            Regards
            Sanjay

            On Wed, Oct 28, 2020, 22:53 Nabelek, John (via IRIS) <
            sac-help-bounce<at>lists.ds.iris.edu> wrote:


            Just multiply by -1.


            On Oct 28, 2020, at 5:58 AM, Sanjay Singh Negi <sonoogeo<at>gmail.com>
            wrote:

            [This email originated from outside of OSU. Use caution with links and
            attachments.]

            Hi John,
            I never thought about it, but logically it seems correct.
            It means that in order to flip, I need to rotate the vertical component
            to 180 degrees.
            Thanks,
            Sanjay


            On Wed, Oct 28, 2020 at 1:31 AM Nabelek, John (via IRIS) <
            sac-help-bounce<at>lists.ds.iris.edu> wrote:
            Sanjay

            To convert right-handed system into left-haded, you will need to flip
            the vertical component.
            For a high-handed system, positive vertical points down.

            -John


            On Oct 27, 2020, at 5:11 AM, Geo . (via IRIS) <
            sac-help-bounce<at>lists.ds.iris.edu> wrote:

            [This email originated from outside of OSU. Use caution with links and
            attachments.]

            Hello Sanjay,
            Based on the SAC documentation, your description of components, and
            assuming that your
            orientation correction is clockwise from north (+80?, how did you
            estimate this?), it seems that "rotate to -80 reverse" is correct.

            "Reverse" indicates that H2 is pointing north and H1 is pointing east:
            the second component is lagging the first by 90°. Think of it as the
            reverse convention as, usually, H1 and H2 are pointing north and east
            respectively.

            http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

            Januka

            On Tuesday, 27 October 2020, sanjay Singh Negi (via IRIS) <
            sac-help-bounce<at>lists.ds.iris.edu> wrote:
            Hi Sac users,
            I have OBS record that follows the right-handed
            system in which H2 component is 90 degree counter-clockwise of H1.

            Horizontal component data file are as following:
            2018.128.01.00.45.420.X.sac ---> East component
            2018.128.01.00.45.420.Y.sac ----> North component
            2018.128.01.00.45.420.Z.sac ----> Vertical component

            The orientation correction angle is 80 degree.

            For rotation, I use the following scheme:
            sac>> read 2018.128.01.00.45.420.Y.sac 2018.128.01.00.45.420.X.sac
            sac>> rotate to 80 reverse


            Could you please comment on whether the command I give is correct or
            not?
            Why I am confused about rotation is because of two following reasons:

            1: To get true north-south rotation for an OBS record the orientation
            correction of 80 degrees has to be made. For this, logically -80/360-80
            degree should be implemented to rotate it back to North-South. Would +80
            degree be fine?

            2. What exactly sac does on applying reverse at the end of rotate
            command?

            Thanks in advance.

            Regards
            Sanjay




            --
            Januka Attanayake
            Research Fellow | Earthquake Seismology
            Homepage: https://sites.google.com/site/janukaattanayake

            School of Earth Sciences | McCoy Bldg. 200
            University of Melbourne | Parkville 3010 VIC
            Australia





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            Topic home: http://ds.iris.edu/message-center/topic/sac-help/ |
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            Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
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            --



            Sanjay Singh Negi
            Alternate Email: sasnegi85<at>gmail.com

            Contact No.- +91-9536145596



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            • Sorry for the delay, but ...

              If one simply flips the vertical, the header variable CMPINC will not be correct
              for that component.

              CMPINC is defined as Component incident angle (degrees from upward vertical)

              To be complete one must change CMPINC for that component to 180 if one
              multiplies it by -1.

              While looking this up in the PDF manual, I found we had inadvertently left out
              the SAC Data File Format in the PDF manual (it is there in the HTML version). 
              That will be fixed shortly.

              Please let me know of any other problems in the PDF/HTML manuals.

              Arthur



              On 10/28/20 2:19 PM, sanjay Singh Negi (via IRIS) wrote:
              Thank you for the correction.

              Regards
              Sanjay

              On Wed, Oct 28, 2020, 22:53 Nabelek, John (via IRIS)
              <sac-help-bounce<at>lists.ds.iris.edu <sac-help-bounce<at>lists.ds.iris.edu>>
              wrote:


              Just multiply by -1.


              On Oct 28, 2020, at 5:58 AM, Sanjay Singh Negi <sonoogeo<at>gmail.com
              <sonoogeo<at>gmail.com>> wrote:

              [This email originated from outside of OSU. Use caution with links and
              attachments.]

              Hi John,
              I never thought about it, but logically it seems correct.
              It means that in order to flip, I need to rotate the vertical component
              to 180 degrees.
              Thanks,
              Sanjay


              On Wed, Oct 28, 2020 at 1:31 AM Nabelek, John (via IRIS)
              <sac-help-bounce<at>lists.ds.iris.edu
              <sac-help-bounce<at>lists.ds.iris.edu>> wrote:
              Sanjay

              To convert right-handed system into left-haded, you will need to flip
              the vertical component.
              For a high-handed system, positive vertical points down.

              -John


              On Oct 27, 2020, at 5:11 AM, Geo . (via IRIS)
              <sac-help-bounce<at>lists.ds.iris.edu
              <sac-help-bounce<at>lists.ds.iris.edu>> wrote:

              [This email originated from outside of OSU. Use caution with links and
              attachments.]

              Hello Sanjay,
              Based on the SAC documentation, your description of components, and
              assuming that your
              orientation correction is clockwise from north (+80?, how did you
              estimate this?), it seems that "rotate to -80 reverse" is correct.

              "Reverse" indicates that H2 is pointing north and H1 is pointing east:
              the second component is lagging the first by 90°. Think of it as the
              reverse convention as, usually, H1 and H2 are pointing north and east
              respectively.

              http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html
              http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

              Januka

              On Tuesday, 27 October 2020, sanjay Singh Negi (via IRIS)
              <sac-help-bounce<at>lists.ds.iris.edu
              <sac-help-bounce<at>lists.ds.iris.edu>> wrote:
              Hi Sac users,
              I have OBS record that follows the right-handed
              system in which H2 component is 90 degree counter-clockwise of H1.

              Horizontal component data file are as following:
              2018.128.01.00.45.420.X.sac   ---> East component
              2018.128.01.00.45.420.Y.sac   ----> North component
              2018.128.01.00.45.420.Z.sac   ----> Vertical component

              The orientation correction angle is 80 degree.

              For rotation, I use the following scheme:
              sac>> read 2018.128.01.00.45.420.Y.sac 2018.128.01.00.45.420.X.sac
              sac>> rotate to 80 reverse


              Could you please comment on whether the command I give is correct or not?
              Why I am confused about rotation is because of two following reasons:

              1: To get true north-south rotation for an OBS record the orientation
              correction of 80 degrees has to be made. For this, logically -80/360-80
              degree should be implemented to rotate it back to North-South. Would +80
              degree be fine?

              2. What exactly sac does on applying reverse at the end of rotate command?

              Thanks in advance.

              Regards
              Sanjay



              • sanjay Singh Negi
                2020-12-04 10:28:58
                Dear Prof. Snoke,
                Thank you for your email. The CMPINC will be
                taken into account.
                I will be glad to contribute and update on any problem related to SAC.

                With warm regards,
                Sanjay


                On Thu, Dec 3, 2020 at 11:46 PM Arthur Snoke (via IRIS) <
                sac-help-bounce<at>lists.ds.iris.edu> wrote:

                Sorry for the delay, but ...

                If one simply flips the vertical, the header variable CMPINC will not be
                correct
                for that component.

                CMPINC is defined as Component incident angle (degrees from upward
                vertical)

                To be complete one must change CMPINC for that component to 180 if one
                multiplies it by -1.

                While looking this up in the PDF manual, I found we had inadvertently left
                out
                the SAC Data File Format in the PDF manual (it is there in the HTML
                version).
                That will be fixed shortly.

                Please let me know of any other problems in the PDF/HTML manuals.

                Arthur



                On 10/28/20 2:19 PM, sanjay Singh Negi (via IRIS) wrote:
                Thank you for the correction.

                Regards
                Sanjay

                On Wed, Oct 28, 2020, 22:53 Nabelek, John (via IRIS)
                <sac-help-bounce<at>lists.ds.iris.edu <mailto:
                sac-help-bounce<at>lists.ds.iris.edu>>
                wrote:


                Just multiply by -1.


                On Oct 28, 2020, at 5:58 AM, Sanjay Singh Negi <sonoogeo<at>gmail.com
                <sonoogeo<at>gmail.com>> wrote:

                [This email originated from outside of OSU. Use caution with links
                and
                attachments.]

                Hi John,
                I never thought about it, but logically it seems correct.
                It means that in order to flip, I need to rotate the vertical
                component
                to 180 degrees.
                Thanks,
                Sanjay


                On Wed, Oct 28, 2020 at 1:31 AM Nabelek, John (via IRIS)
                <sac-help-bounce<at>lists.ds.iris.edu
                <sac-help-bounce<at>lists.ds.iris.edu>> wrote:
                Sanjay

                To convert right-handed system into left-haded, you will need to
                flip
                the vertical component.
                For a high-handed system, positive vertical points down.

                -John


                On Oct 27, 2020, at 5:11 AM, Geo . (via IRIS)
                <sac-help-bounce<at>lists.ds.iris.edu
                <sac-help-bounce<at>lists.ds.iris.edu>> wrote:

                [This email originated from outside of OSU. Use caution with
                links and
                attachments.]

                Hello Sanjay,
                Based on the SAC documentation, your description of components,
                and
                assuming that your
                orientation correction is clockwise from north (+80?, how did you
                estimate this?), it seems that "rotate to -80 reverse" is correct.

                "Reverse" indicates that H2 is pointing north and H1 is pointing
                east:
                the second component is lagging the first by 90°. Think of it as the
                reverse convention as, usually, H1 and H2 are pointing north and east
                respectively.

                http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html
                http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

                Januka

                On Tuesday, 27 October 2020, sanjay Singh Negi (via IRIS)
                <sac-help-bounce<at>lists.ds.iris.edu
                <sac-help-bounce<at>lists.ds.iris.edu>> wrote:
                Hi Sac users,
                I have OBS record that follows the
                right-handed
                system in which H2 component is 90 degree counter-clockwise of H1.

                Horizontal component data file are as following:
                2018.128.01.00.45.420.X.sac ---> East component
                2018.128.01.00.45.420.Y.sac ----> North component
                2018.128.01.00.45.420.Z.sac ----> Vertical component

                The orientation correction angle is 80 degree.

                For rotation, I use the following scheme:
                sac>> read 2018.128.01.00.45.420.Y.sac
                2018.128.01.00.45.420.X.sac
                sac>> rotate to 80 reverse


                Could you please comment on whether the command I give is
                correct or not?
                Why I am confused about rotation is because of two following
                reasons:

                1: To get true north-south rotation for an OBS record the
                orientation
                correction of 80 degrees has to be made. For this, logically
                -80/360-80
                degree should be implemented to rotate it back to North-South. Would
                +80
                degree be fine?

                2. What exactly sac does on applying reverse at the end of
                rotate command?

                Thanks in advance.

                Regards
                Sanjay



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                --



                Sanjay Singh Negi
                Alternate Email: sasnegi85<at>gmail.com

                Contact No.- +91-9536145596

12:35:36 v.b31bec54